Transformer



Oct. 20, 1936. H. T. FAUS ET AL 2,058,302

TRANSFORMER Filed Feb. 18, 1936 Fig. l.

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/7 '1 TRANSFORMER MIG/VETONOflI/E FOR6 Inventors: 3 Harold T. Faus, Almon J.Coron,

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Patented Oct. 20, 1936 UNITED STATES PATENT OFFICE TRANSFORMERApplication February 18, 1936. Serial No. 64.494

2 Claims. (Cl. 171-119) Our invention relates to transformers. Thevoltage of a generator is not always constant for any given speed of thegenerator because the magnetic characteristics of the generator maychange with age and the voltage of the generator may be affected bychanges in the temperature of the windings. An indicating instrumentresponsive to changes in the generator voltage cannot be relied upon toindicate its speed accurately. The frequency of the generator, however,is always exactly proportional to its speed and in order that theinstrument may give accurate indications of the speed it has beenproposed to interpose between the generator and the instrument atransformer having such characteristics that its secondary voltage isindependent of changes in its primary voltage and therefore of changesin the generator voltage. but is substantially proportional to thegenerator frequency so that the instrument may indicate with substantialaccuracy the frequency and therefore the speed of the generator. Such atransformer is disclosed in the United States Patent No. 1,835,969 to A.J. Rohner, issued December 8, 1931, and assigned to the General ElectricCompany.

The general object of the present invention is to provide an improvedtransformer having such characteristics that throughout its operatingrange its secondary voltage will be independent of changes in itsprimary voltage, but will be very exactly proportional to the frequencyof its primary voltage.

The invention will be better understood from the following descriptiontaken in connection with the accompanying drawing in which Fig. 1 showsa transformer constructed in accordance with the invention and connectedbetween a generator and an instrument for indicating the generatorfrequency and speed; Fig. 2 is a perspective view of the magnetic coreof the transformer; Fig. 3 is an explanatory diagram; and Fig. 4 shows amodified form of the invention.

Like reference characters indicate similar parts in the diflerentfigures of the drawing.

The transformer ll shown in P18. 1 has a magnetic core ll having twoinner winding legs I! and ii, a primary winding ll surrounding bothwinding legs and two secondary windings II and II surrounding thewinding legs I! and I! respectively. The transformer is of the shelltype with outside legs I! and II providing return paths for the magneticflux in the winding legs I! and i3 and surrounding these winding legsand the primary and secondary windings i4, II and II.

The secondary windings l5 and it are connected in series with theirvoltages opposed. The primary winding It is connected to the windings itof the generator I. The alternating voltage is induced in the generatorwindings It by rotation 5 of the rotor 2|. The secondary windings l8 andii of the transformer are connected through a high resistance 22 and afull wave rectifier 23 to an indicating instrument 2!. The rectifier IIpermits the use of a direct current indicating 10 instrument which ispreferable to one of the alternating current type because of its moreuniform scale division. The resistances of the secondary windings i5 andI of the transformer and of the indicating instrument It tend to varydirectly with changes in their temperatures and the resistance of therectifier 23 will probably change inversely with temperature changes.The change in resistance of the rectifier 23 is usually greater than thecombined change in resistance of the secondary windings I! and it and ofthe indicating instrument 24. The resistance 22 may have a slightnegative temperature coemcient to compensate for the resistance changesin the windings I5 and it and in the rectifier 23 and 25 instrument 2|,and its resistance should be very hi h so that the resistance of theentire circuit will be high compared to its reactance. A resistance 25having a slight negative temperature coefllcient may be connected acrossthe instrument 2 to compensate for errors due to changes in thetemperature of the instrument.

The alternating voltage of the generator windings ll forces alternatingcurrent through the primary winding ll of the transformer i0 and thisproduces an alternating magnetomotive force in the transformer core.This magnetomotive force will of course increase and decrease with thespeed of the generator. The resultant voltage of the secondary windingsl5 and II is equal to the difference between the two voltages becausethey are connected with their voltages opp e It will be assumed that thenumber of turns is the same in both windings l5 and ii.

Fig. 3 shows the relation between the transformer magnetomotive forceand the transformer core flux. The winding leg i2 is preferably formedof magnetic material having very high permeability such as any one ofthe well known nickel-iron alloys. The winding leg I! is formed of twosmall strips of material of very small cross section held againstopposite faces of the ends of the core by the secondary winding l8surrounding them. Ihe winding it is also held in place by the two stripsforming its winding leg.

The magnetomotive force produced by the primary winding ll induces amagnetic force in the winding leg l2, this flux following a return paththrough the outer legs l1 and I8 of the core. This magnetic flux in thewinding leg I! may be represented by the curve A of Fig. 3. The primarywinding ll produces a magnetomotive force which would induce a magneticflux represented by the curve B of Fig.3 if the reluctance of itswinding leg l3 were the same as that of air. At least one of the stripsforming this winding leg l3, however, is of magnetic material so thatthe reluctance of this winding leg is slightly less than that of air anda slightly larger magnetic flux is induced as indicated by the curve Cof Fig. 3. It has been found desirable to form one of the strips of thewinding leg l3 of soft iron and the other strip of some material, suchas brass, having substantially the same permeability as that of air. Ithas been found that the provision of the small magnetic strip formingpart of the winding leg i3 will cause the curves A and C to be almostexactly parallel for all values of flux corresponding to a considerablerange of magnetomotive force above that which produces saturation in thewinding leg l2. It has heretofore been assumed that in transformers ofthis type the reluctance of magnetic material is substantially that ofair for any value of magnetomotive force above that capable of producingsaturation. This is approximately so but it has been found in connectionwith the present invention that changes in magnetic flux in the twowinding legs I! and I3 are more nearly exactly equal for a given changein magnetomotive force if the reluctance of the winding leg 13 isslightly decreased by providing a strip of magnetic material of verysmall cross section, as has already been described.

The resultant voltage of the two secondary windings l'5 and I6 is equalto the difference between their two voltages. The voltage induced in thesecondary winding I is equal to 4FN where F and 1p representrespectively the frequency and maximum value of the magnetic flux in thewinding I2 and N represents the number of turns in the winding I5. Thevoltage induced in the secodary winding I6 is equal to 4FN 10 where Fand o represent respectively the frequency and maximum value of themagnetic flux in the winding leg H and N represents the number of turnsin the secondary winding IS. The value of F is the same for bothwindings and the value of N has been assumed to be the same for bothwindings and therefore the resultant voltage of the windings l5 and iliis equal to 4FNl0"( It will be seen from Fig. 3 that for all values ofmagnetic flux above that corresponding to saturation of the winding legii, the difference between the values of the magnetic fluxes in the twowinding legs is constant and may be represented by the curve L. Theresultant voltage of the two windings I5 and I6 is therefore equal to4FNL10 for all values of magnetomotive force above that corresponding tosaturation of the winding leg l2 and therefore corresponding to aconsiderable variation in the frequency and speed of the generator 20.Inasmuch as the values of N and L are both constant, it follows that thevoltage of the secondary windings l5 and i6 is exactlyproportional tothe frequencyof thevoltage and to the speed of the generator 20. Thesecondary voltage of the transformer lil is thus directly proportionalto the frequency of its primary voltage and is independent of changes inthe value of its primary voltage throughout a considerable range ofvalues. The indicating instrument 2| may therefore be calibrated toindicate directly the frequency of the voltage of the primary circuit ofthe transformer Ill or of the speed of a generator for supplying currentto the primary side of the transformer.

The modified form of the transformer shown in Fig. 4 is similar to thatshown in Figs. 1 and 2 except that the two winding legs I! and 13 aremerged together beyond their respective windings to form a singlemagnetic path around which is wound the primary winding II. In bothforms of the transformer shown in Figs. 1, 2 and 4 the transformerwindings are surrounded by the outside legs and I8 and the yokes 26which connect the ends of the outside legs to the ends of the windinglegs. The outside legs i1 and Ill and the yokes 26 thus shield thewindings from outside influences which might otherwise causedisturbances in them and inaccuracy of the indications of the instrument24.

The invention has been explained by describing and illustrating twoforms thereof and it will be apparent that changes may be made withoutdeparting from the spirit of the invention and the scope of the appendedclaims.

What we claim as new and desire to secure by Letters Patent of theUnited States, is,--

1. A transformer including two magnetic winding legs of widely diflerentmagnetic properties, one of said winding legs being formed of nickelironalloy and the other winding leg including a thin strip of soft iron, asecondary winding surrounding each winding leg. a primary windingsurrounding both winding legs, said secondary windings being connectedin series with their voltages opposed, and outer magnetic legs and yokessurrounding said windings and winding legs.

2. A transformer including two magnetic winding legs of widely diiferentmagnetic properties, a secondary winding surrounding each winding leg, aprimary winding surrounding both winding legs, said second windingsbeing connected in series with their voltages opposed, and outermagnetic legs and yokes surrounding said windings and winding legs, oneof said winding legs including two strips disposed against oppositesides of said yokes, and at least one of said strips being of magneticmaterial of small cross section.

HAROLD T. FAUS. ALMON J. CORSON.

CERTIFICATE OF CORRECTION.

Patent No. 2,058,302. October 20, 1936.

HAROLD T. FAUS, ET AL.

It is hereby certified that error appears in the printed specificationof the above numbered patent requiring correction as follows: Page 2,second column, line 55, claim 2, for "second" read secondary; and thatthe said Letters Patent should be read with this correction therein thatthe same may conform to the record of the case in the Patent Office.

Signed and sealed this 29th day of December, A. D. 1936.

Henry Van Aredeie (Seal) Acting Commissioner of Patents,

